Photoelectric conversion device and manufacturing method thereof

ABSTRACT

It is an object to provide a photoelectric conversion device which detects light ranging from weak light to strong light. The present invention relates to a photoelectric conversion device having a photodiode having a photoelectric conversion layer, an amplifier circuit including a thin film transistor and a bias switching means, where a bias which is connected to the photodiode and the amplifier circuit is switched by the bias switching means when intensity of incident light exceeds predetermined intensity, and accordingly, light which is less than the predetermined intensity is detected by the photodiode and light which is more than the predetermined intensity is detected by the thin film transistor of the amplifier circuit. By the present invention, light ranging from weak light to strong light can be detected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photoelectric conversion device, andparticularly relates to a photoelectric conversion device including athin film semiconductor element and a manufacturing method thereof. Inaddition, the present invention relates to an electronic device using aphotoelectric conversion device.

2. Description of the Related Art

A number of photoelectric conversion devices used for detecting anelectromagnetic wave are generally known, for example, a photoelectricconversion device which has sensitivity from ultra-violet rays toinfrared rays is referred to as a light sensor in general. A lightsensor which has sensitivity to a visible light region with a wavelengthof 400 to 700 nm is particularly referred to as a visible light sensor,and a number of visible light sensors are used for devices which needilluminance adjustment, on/off control, or the like depending on a humanliving environment.

In particular, in a display device, brightness of the periphery of thedisplay device is detected to adjust the display luminance. It isbecause unnecessary electric power can be reduced by detecting theperipheral brightness and obtaining appropriate display luminance. Forexample, a light sensor for such adjustment of luminance is used for acell phone or a personal computer.

In addition, not only peripheral brightness but also luminance ofbacklight of a display device, particularly, a liquid crystal displaydevice is also detected by a light sensor to adjust luminance of adisplay screen.

In such a light sensor, a photodiode is used for a sensing part and anoutput current of the photodiode is amplified in an amplifier circuit.As such an amplifier circuit, for example, a current mirror circuit isused (Patent Document 1).

[Patent Document 1] Patent Document No. 3444093

SUMMARY OF THE INVENTION

By a conventional light sensor, weak light can be detected; however,there is a problem that a range of an output current is expanded andvoltage used for one gray-scale is lowered when light, from weak lightto strong light, is detected.

A photoelectric conversion device of the present invention has aphotodiode including a photoelectric conversion layer, a current mirrorof a TFT and a bias switching means. In the photoelectric conversiondevice of the present invention, the current mirror circuit isirradiated with light, and functions as a second light sensor at thetime of forward bias. Note that the bias switching means may beconstituted by a circuit.

According to the present invention, weak light can be detected by aphotodiode and light having certain illuminance or more can be detectedby a TFT. Accordingly, an output current can be reduced once, a range ofan absolute value of the output current can be narrowed, and a voltagevalue of one gray-scale can be increased.

The present invention relates to a photoelectric conversion devicehaving a photodiode including a photoelectric conversion layer, anamplifier circuit including a thin film transistor and a bias switchingmeans, where a bias which is connected to the photodiode and theamplifier circuit is switched by the bias switching circuit at apredetermined intensity of incident light, and light which is less thanthe predetermined intensity is detected by the photodiode and lightwhich is more than the predetermined intensity is detected by the thinfilm transistor of the amplifier circuit.

The present invention relates to a driving method of a photoelectricconversion device having a photodiode including a photoelectricconversion layer, an amplifier circuit including a thin film transistorand a bias switching means, the method comprising the steps of:switching a bias which is connected to the photodiode and the amplifiercircuit by the bias switching circuit at a predetermined intensity ofincident light, and detecting light which is less than the predeterminedintensity by the photodiode or light which is more than thepredetermined intensity by the thin film transistor of the amplifiercircuit.

In the present invention, the photoelectric conversion layer has ap-type semiconductor layer, an i-type semiconductor layer and an n-typesemiconductor layer.

In the present invention, the thin film transistor has a source regionor a drain region, a channel formation region, a gate insulating film,and a gate electrode.

In the present invention, the photodiode and the amplifier circuit isformed over a light-transmitting substrate.

In the present invention, a direction of incident light which isdetected by the photodiode is the same as a direction of incident lightwhich is detected by the thin film transistor.

In the present invention, the thin film transistor is a top gate thinfilm transistor.

In the present invention, with a substrate as the center, a direction ofincident light which is detected by the photodiode and a direction ofincident light which is detected by the thin film transistor areopposite to each other.

In the present invention, the thin film transistor is a bottom gate thinfilm transistor.

According to the present invention, by detecting weak light by aphotodiode and detecting strong light by a TFT, a wide range of lightintensity can be detected.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are diagrams each showing a photoelectric conversiondevice of the present invention;

FIG. 2 is a diagram showing one example of a current mirror circuit ofthe present invention;

FIG. 3 is a diagram showing one example of a current mirror circuit ofthe present invention;

FIGS. 4A and 4B are cross-sectional views of a photoelectric conversiondevice of the present invention;

FIGS. 5A to 5D are views each showing a manufacturing process of aphotoelectric conversion device of the present invention;

FIGS. 6A to 6C are views each showing a manufacturing process of aphotoelectric conversion device of the present invention;

FIGS. 7A to 7C are views each showing a manufacturing process of aphotoelectric conversion device of the present invention;

FIGS. 8A and 8B are cross-sectional views of a photoelectric conversiondevice of the present invention;

FIGS. 9A to 9E are views each showing a manufacturing process of aphotoelectric conversion device of the present invention;

FIGS. 10A to 10C are views each showing a manufacturing process of aphotoelectric conversion device of the present invention;

FIG. 11 is a cross-sectional view of a photoelectric conversion deviceof the present invention;

FIGS. 12A and 12B are cross-sectional views of a photoelectricconversion device of the present invention;

FIGS. 13A and 13B are cross-sectional views of a photoelectricconversion device of the present invention;

FIG. 14 is a view showing a device on which a photoelectric conversiondevice of the present invention is mounted;

FIGS. 15A and 15B are views each showing a device on which aphotoelectric conversion device of the present invention is mounted;

FIGS. 16A and 16B are views each showing a device on which aphotoelectric conversion device of the present invention is mounted;

FIG. 17 is a view showing a device on which a photoelectric conversiondevice of the present invention is mounted;

FIGS. 18A and 18B are views each showing a device on which aphotoelectric conversion device of the present invention is mounted;

FIG. 19 is a view showing illuminance dependence of an output current ina photoelectric conversion device of the present invention;

FIGS. 20A and 20B are views each showing illuminance dependence of anoutput current in a photoelectric conversion device of the presentinvention;

FIG. 21 is a view showing illuminance dependence of an output current ina photoelectric conversion device of the present invention;

FIG. 22 is a diagram showing a circuit configuration of a circuit whichswitches a power source (bias) of the present invention;

FIG. 23 is a diagram showing a circuit configuration of a circuit whichswitches a power source (bias) of the present invention;

FIG. 24 is a view showing comparisons of relative sensitivity of aphotoelectric conversion device of the present invention, relativesensitivity of a TFT using a polycrystalline silicon film, relativesensitivity of single crystal silicon and standard luminous efficiency.

FIGS. 25A and 25B are views each showing a circuit configuration of acircuit which switches a power source (bias) of the present invention;

FIGS. 26A and 26B are views each showing a circuit configuration of acircuit which switches a power source (bias) of the present invention;and

FIGS. 27A and 27B are views each showing a circuit configuration of acircuit which switches a power source (bias) of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[Best Mode for Carrying Out the Invention]

Hereinafter, embodiment mode of the present invention will be describedbased on the accompanying drawings. However, the present invention canbe carried out in many different modes, and it is easily understood bythose skilled in the art that modes and details herein disclosed can bemodified in various ways without departing from the spirit and the scopeof the present invention. Therefore, the present invention is notlimited to the description of the embodiment mode to be given below.Note that in all drawings for describing the embodiment mode, the samereference numerals are used for the same portions or the portions havinga similar function, and the repeated description thereof is omitted.

This embodiment mode will be described with reference to FIGS. 1A and1B, FIG. 2, FIG. 3, FIGS. 4A and 4B, and FIG. 21.

As shown in FIGS. 1A and 1B, a photoelectric conversion device of thepresent application has a photo IC (Integrated circuit) 101, a powersource switching means 102, a power source 103, an output terminal V₀,and a connecting resistor R_(L), and the photo IC (photo integratedcircuit) 101 has a thin film integrated circuit constituted by aphotoelectric conversion element 115 (a first photo sensor) and a TFT (asecond photo sensor). The thin film integrated circuit is constituted bya current mirror circuit 114 including n-channel thin film transistors(TFT) 112 and 113. In addition, the photoelectric conversion element 115and the current mirror circuit 114 are connected to terminal electrodes121 and 122, and a photoelectric current is extracted through theseterminal electrodes 121 and 122 (FIG. 1B).

The current mirror circuit 114 functions to amplify an output value ofthe photoelectric conversion element 115 when intensity of incidentlight is low. In addition, when intensity of incident light is high, then-channel TFTs 112 and 113 become a photoelectric current source, and agenerated photoelectric current is extracted through the terminalelectrodes 121 and 122.

In FIG. 1B, two TFTs are illustrated. However, for example, in order toincrease an output value by 100 times, one n-channel TFT 112 and 100n-channel TFTs 113 may be provided (FIG. 2). Note that, in FIG. 2, sameportions as those in FIGS. 1A and 1B are denoted by the same referencenumerals. In FIG. 2, an n-channel TFT 113 is constituted by 100n-channel TFTs 113 a, 113 b, 113 c, 113 d . . . . Accordingly, aphotoelectric current generated in the photoelectric conversion element115 is amplified by 100 times to be outputted.

FIG. 1B shows an equivalent circuit diagram of the current mirrorcircuit 114 using an n-channel TFT; however, only a p-channel TFT may beused instead of the n-channel TFT.

Note that, in a case where an amplifier circuit is formed from ap-channel TFT, an equivalent circuit shown in FIG. 3 is obtained. InFIG. 3, terminal electrodes 221 and 222 correspond to the terminalelectrodes 121 and 122 of FIG. 1B, respectively, and each of theterminal electrodes 221 and 222 may connect a photoelectric conversionelement 204, p-channel TFTs 201 and 202 as shown in FIG. 3.

A cross-sectional view of the photo IC 101 of FIG. 1B is shown in FIGS.4A and 4B.

In FIG. 4A, reference numeral 310 denotes a substrate; 312, a baseinsulating film; and 313, a gate insulating film. Since received lightpasses through the substrate 310, the base insulating film 312 and thegate insulating film 313, materials having high light-transmittingproperty are preferably used as the materials for all of these.

A photoelectric conversion element has a wiring 319; a protectiveelectrode 318; a p-type semiconductor layer 111 p, an n-typesemiconductor layer 111 n and an intrinsic (i-type) semiconductor layer111 i which is sandwiched between the p-type semiconductor layer 111 pand the n-type semiconductor layer 111 n, each of which is part of aphotoelectric conversion layer 111; and a terminal electrode 121.

The p-type semiconductor layer 111 p may be formed by depositing asemiamorphous silicon film containing an impurity element belonging toGroup 13 of the periodic table, for example, boron (B) by a plasma CVDmethod.

Note that a semiamorphous semiconductor film includes semiconductorwhich has an intermediate structure between an amorphous semiconductorand a crystalline semiconductor having a crystalline structure(including a single crystal and a polycrystal). The semiamorphoussemiconductor film has a third condition which is stable in terms offree energy, and is a crystalline substance having a short-range orderand lattice distortion, and the crystal grain size of 0.5 to 20 nm ofwhich can be dispersed in a non-single crystalline semiconductor film.As for the semiamorphous semiconductor film, raman spectrum thereof isshifted to a wavenumber side lower than 520 cm⁻¹, and the diffractionpeaks of (111) and (220) that are said to be caused by a Si crystallattice are observed in X-ray diffraction. In addition, thesemiamorphous semiconductor film contains hydrogen or halogen of atleast 1 atom % or more to terminate a dangling bond. In the presentspecification, such a semiconductor film is referred to as asemiamorphous semiconductor (SAS) film for the sake of convenience.Moreover, a noble gas element such as helium, argon, krypton or neon iscontained to further promote lattice distortion so that stability isenhanced and a favorable semiamorphous semiconductor film is obtained.Note that a microcrystalline semiconductor film (microcrystal film) isalso included in the semiamorphous semiconductor film.

Also, the SAS film can be obtained by glow discharge decomposition ofgas containing silicon. As typical gas containing silicon, SiH₄ isgiven, and in addition, Si₂H₆, SiH₂Cl₂, SiHCl₃, SiC₄, SiF₄, or the likecan also be used. The gas containing silicon is diluted with hydrogen,or gas in which one or more of noble gas elements of helium, argon,krypton and neon are added to hydrogen; thereby, the SAS film can beformed easily. It is preferable that the dilution ratio is set to be ina range of 2 to 1000 times. Moreover, carbide gas such as CH₄ or C₂H₆,germanium gas such as GeH₄ or GeF₄, F₂, or the like may be mixed in thegas containing silicon to adjust an energy band width to be 1.5 to 2.4eV or 0.9 to 1.1 eV.

After the p-type semiconductor layer 111 p is formed, a semiconductorlayer which does not contain an impurity imparting a conductivity type(referred to as an intrinsic semiconductor layer or an i-typesemiconductor layer) 111 i and the n-type semiconductor layer 111 n aresequentially formed. Accordingly, the photoelectric conversion layer 111including the p-type semiconductor layer 111 p, the i-type semiconductorlayer 111, and the n-type semiconductor layer 111 n is formed.

Note that, in the present specification, the i-type semiconductor layerindicates a semiconductor layer in which concentration of an impurityimparting p-type or n-type is 1×10²⁰ cm⁻³ or less, concentration ofoxygen and nitrogen is 5×10¹⁹ cm⁻³ or less, and photoconductivity todark conductivity is 1000 times or more. In addition, 10 to 1000 ppm ofboron (B) may also be added to the i-type semiconductor layer.

As the i-type semiconductor layer 111 i, for example, a semiamorphoussilicon film may be formed by a plasma CVD method. In addition, as then-type semiconductor layer 111 n, a semiamorphous silicon filmcontaining an impurity element belonging to Group 15 of the periodictable, for example, boron (B) may be formed, and alternatively, animpurity element belonging to Group 15 of the periodic table may beintroduced after the semiamorphous silicon film is formed.

As the p-type semiconductor layer 111 p, the intrinsic semiconductorlayer 111 i and the n-type semiconductor layer 111 n, not only asemiamorphous semiconductor film, but also an amorphous semiconductorfilm may be used.

Each of the wiring 319, a connection electrode 320, a terminal electrode351, a source electrode or a drain electrode 341 of a TFT 113 and asource electrode or a drain electrode 342 of a TFT 112 has a stackedlayer structure of a refractory metal film and a low resistance metalfilm (such as an aluminum alloy or pure aluminum). Here, the wiring 319has a three-layer structure in which a titanium film (Ti film), analuminum film (Al film) and a Ti film are sequentially stacked.

Moreover, protective electrodes 318, 345, 348, 346 and 347 are formed soas to cover the wiring 319, the connection electrode 320, the terminalelectrode 351, the source electrode or the drain electrode 341 of theTFT 113 and the source electrode or the drain electrode 342 of the TFT112, respectively.

In etching the photoelectric conversion layer 111, the wiring 319 isprotected by the protective electrode 318 which covers the wiring 319.As a material for the protective electrode 318, a conductive materialhaving slower etching speed to etching gas (or etchant) for thephotoelectric conversion layer 111 than the photoelectric conversionlayer is preferable. In addition, a conductive material which does notreact with the photoelectric conversion layer 111 to become alloy ispreferable as the material for the protective electrode 318. Note thatthe other protective electrodes 345, 348, 346 and 347 are also formed bythe similar material and manufacturing process to the protectiveelectrode 318.

Also, a structure in which the protective electrodes 318, 345, 348, 346and 347 are not formed over the wiring 319, the connection electrode320, and the terminal electrode 351 may be employed. A visible lightdetective portion having such a structure is shown in FIG. 4B. In FIG.4B, each of a wiring 404, a connection electrode 405, a terminalelectrode 401, a source electrode or a drain electrode 402 of a TFT 112,and a source electrode or a drain electrode 403 of a TFT 113 is formedfrom a single-layer conductive film, and as such a conductive film, atitanium film (Ti film) is preferable. In addition, a single-layer filmformed from an element selected from tungsten (W), tantalum (Ta),molybdenum (Mo), neodymium (Nd), cobalt (Co), zirconium (Zr), zinc (Zn),ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir),and platinum (Pt), an alloy material or a compound material containingthe above element as its main component, or a single-layer film formedfrom nitride of these elements, for example, titanium nitride, tungstennitride, tantalum nitride, or molybdenum nitride can be used instead ofthe titanium film. The number of deposition can be reduced in amanufacturing process by forming the wiring 404, the connectionelectrode 405, the terminal electrode 401, the source electrode or thedrain electrode 402 of the TFT 112, and the source electrode or thedrain electrode 403 of the TFT 113 with a single-layer film.

In FIGS. 4A and 4B, an example of a top gate TFT of a structure in whichthe n-channel TFTs 112 and 113 include one channel formation region (inthis specification, referred to as a single gate structure) is shown;however, a structure having a plurality of channel formation regions mayalso be used to reduce variation in the ON current value. In order toreduce the OFF current value, a lightly doped drain (LDD) region may beprovided in the n-channel TFTs 112 and 113. The LDD region is a regionto which an impurity element is added at low concentration between achannel formation region and a source region or a drain region which isformed by being added with an impurity element at high concentration. Byproviding the LDD region, effect to reduce an electric field in thevicinity of the drain region and prevent deterioration due to hotcarrier injection can be obtained. In addition, in order to preventdeterioration of the ON current value due to hot carrier, the n-channelTFTs 112 and 113 may have a structure in which an LDD region and a gateelectrode are placed so as to be overlapped with each other through agate insulating film (in the present specification, referred to as aGOLD (Gate-drain Overlapped LDD) structure).

In a case of where a GOLD structure is used, effect to reduce anelectric field in the vicinity of a drain region and preventdeterioration due to hot carrier injection is more enhanced than in acase where an LDD region and a gate electrode are not overlapped witheach other. By employing such a GOLD structure, electric field intensityin the vicinity of a drain region is reduced and hot carrier injectionis prevented, and thereby, it is effective for prevention ofdeterioration phenomenon.

The TFTs 112 and 113 included in the current mirror circuit 114 may benot only a top gate TFT but also a bottom gate TFT, for example, aninversely staggered TFT. In this case, it is preferable that a gateelectrode has a light-transmitting property so as not to preventreceived light.

In addition, a wiring 314 is connected to the wiring 319, and alsobecomes a gate electrode extending to an upper side of the channelformation region of the TFT 113 of the amplifier circuit.

A wiring 315 is connected to the n-type semiconductor layer 111 n, andis connected to a drain wiring (also referred to as a drain electrode)or a source wiring (also referred to as a source electrode) of the TFT112. Reference numerals 316 and 317 denote an insulating film and 320denotes a connection electrode. Since light which is received passesthrough the insulating films 316 and 317, a material having highlight-transmitting property is preferably used as the materials for allof these. Note that as the insulating film 317, silicon oxide (SiOx)film which is formed by a CVD method is preferably used. When theinsulating film 317 is formed of a silicon oxide film which is formed bya CVD method, fixing intensity is improved.

In addition, a terminal electrode 350 is formed by the same process asthe wirings 314 and 315, and the terminal electrode 351 is formed by thesame process as the wiring 319 and the connection electrode 320.

A terminal electrode 121 is connected to the n-channel semiconductorlayer 111 n, and is mounted on an electrode 361 of a substrate 360 by asolder 364. A terminal electrode 122 is formed by the same process asthe terminal electrode 121, and is mounted on an electrode 362 of thesubstrate 360 by a solder 363 (FIG. 4A).

In FIGS. 4A and 4B, as shown by arrows in the drawings, light entersisland shaped semiconductor regions of the photoelectric conversionlayer 111 and the TFTs 112 and 113 from the substrate 310 side.Accordingly, a photoelectric current is generated, and light can bedetected.

However, although not shown, light enters not only from the direction ofthe arrows but also from the opposite side, that is, the substrate 360side. The incident light passes through a sealing layer 324 and does notpass through the electrode and the wiring that shield light to enter theisland-shaped semiconductor regions of the photoelectric conversionlayer 111 and TFTs 112 and 113; accordingly, a photoelectric current canbe generated.

By using the switching means 102, intensity of light reverses bias tothe whole circuit on reaching a predetermined intensity. In a case ofsimply reversing, a power source may be one kind; however, differentbias may be applied by using two different kinds of the power source 103as shown in FIG. 1A. In addition, an output voltage which is applied tothe connecting resistor R is also reversed; therefore, a switching means(not shown) by which the output voltage is reversed may also be used.

A relation between illuminance L and an absolute value of an outputcurrent (photoelectric current) I is shown in FIG. 21. Note that theabsolute value of the output current I is plotted because an outputcurrent direction from a photodiode and an output current direction froma TFT are opposite to each other. In a case where the illuminance islower than L₁, bias may be adjusted so as to detect light which entersthe photoelectric conversion layer 111, and in a case where theilluminance is higher than L₁, bias may be reversed so as to detectlight which enters the TFTs 112 and 113. By the operation as describedabove, a wide range of illuminance can be detected even when an outputcurrent range is small.

Embodiment 1

This embodiment will be described with reference to FIG. 19, FIGS. 20Aand 20B, and FIG. 22.

In FIG. 19 and FIGS. 20A and 20B, illuminance dependence of an outputcurrent in a photoelectric conversion device manufactured by the presentinvention is shown.

In FIG. 19, ELC denotes illuminance dependence of an output current in aphotoelectric conversion device having a current mirror circuit by a TFTin which an island-shaped semiconductor region is crystallized by anexcimer laser. Also, CW denotes illuminance dependence of an outputcurrent in a photoelectric conversion device in which a current mirrorcircuit is formed by a TFT in which an island-shaped semiconductorregion is crystallized by a continuous wave laser. In FIGS. 20A and 20B,ELC and CW which are separately plotted are shown. In addition, aforward direction and an opposite direction denote a direction of bias.

A difference in illuminance dependence of an output current between theTFT having an island-shaped semiconductor region which is crystallizedby the excimer laser and the TFT having an island-shaped semiconductorregion which is crystallized by the continuous wave laser is derivedfrom a difference in crystallinity of the island-shaped semiconductorregions. Also, the illuminance dependence can be changed depending on achannel formation region of a TF and a threshold value.

In a case of ELC, a range of an output current becomes 20 nA to 5 μA,and a range of detected illuminance becomes 0.5 to 100,000 1× by settinga predetermine intensity to be approximately 100 1×. In a case of usingELC in the circuit of FIG. 1A, by setting the connecting resistor R_(L)to be 400 kΩ, an output voltage is changed from 0.08 to 2 V, and adigital conversion can be performed with 8 bit (256 grayscale levels).

In FIG. 24, a plot in which the photo IC 101 shown in FIGS. 1A and 1B ofthe present invention, a TFT using a polycrystalline silicon film(hereinafter, referred to as a poly-Si TFT), single crystalline silicon(hereinafter, referred to as cry-Si), and standard luminous efficiencyare compared is shown.

In FIG. 24, relative sensitivity of the photo IC of the presentinvention is shown by a solid line, standard luminous efficiency factoris shown by a dashed line, relative sensitivity of the poly-Si TFT isshown by a line interrupted by two dots, and relative sensitivity ofcry-Si is shown by a line interrupted by a single dot. According to FIG.24, the relative sensitivity of the photo IC of the present invention isextremely close to the standard luminous efficiency factor, in otherwords, luminosity close to human eyes can be obtained by the photo IC ofthe present invention.

Embodiment 2

This embodiment will be described with reference to FIGS. 4A and 4B,FIGS. 5A to 5D, FIGS. 6A to 6C, and FIGS. 7A to 7C. Note that the sameportions as those described in Best Mode for Carrying Out the Inventionare denoted by the same reference numerals.

First, an element is formed over a substrate (a first substrate 310).Here, AN 100 which is one of glass substrates is used as the substrate310.

Subsequently, a silicon oxide film containing nitrogen (with a thicknessof 100 nm) which becomes a base insulating film 312 is formed by aplasma CVD method, and a semiconductor film, for example, an amorphoussilicon film containing hydrogen (with a thickness of 54 nm) is formedto be stacked thereover without being exposed to the air. Also, the baseinsulating film 312 may be a stacked layer using a silicon oxide film, asilicon nitride film and a silicon oxide film containing nitrogen. Forexample, as the base insulating film 312, a film in which a siliconnitride film containing oxygen with a thickness of 50 nm and further asilicon oxide film containing nitrogen with a thickness of 100 nm arestacked may also be formed. Note that a silicon oxide film containingnitrogen or a silicon nitride film functions as a blocking layer whichprevents impurity dispersion of alkali metal from a glass substrate.

Next, the above amorphous silicon film is crystallized by a knowntechnique (a solid phase growth method, a laser crystallization method,a crystallization method using catalytic metal, or the like) to form asemiconductor film having a crystal structure (a crystallinesemiconductor film), for example, a polycrystalline silicon film. Here,a polycrystalline silicon film is obtained by a crystallization methodusing catalytic metal. Nickel acetate solution containing 10 ppm ofnickel which is converted into weight is applied by a spinner. Note thata method by which a nickel element is diffused over the entire surfaceby a sputtering method may be used instead of the application. Then,heat treatment is performed and crystallization is performed to form asemiconductor film having a crystalline structure (here, apolycrystalline silicon film). Here, after heat treatment (500° C., anhour), heat treatment for crystallization (550° C., 4 hours) isperformed to obtain a polycrystalline silicon film.

Subsequently, an oxide film on the surface of the polycrystallinesilicon film is removed with rare hydrofluoric acid or the like.Thereafter, laser light (XeCl: wavelength of 308 nm) irradiation toincrease degree of crystallinity and repair a defect which is left inthe crystal grain is performed in the air or in an oxygen atmosphere.

As the laser light, an excimer laser having a wavelength of 400 nm orless, or a second harmonic wave or a third harmonic wave of a YAG laseris used. Here, pulse laser light with repetition rate of approximately10 to 1000 Hz is used, the laser light is converged to be 100 to 500mJ/cm² with an optical system, and irradiation is performed with overlaprate of 90 to 95% to scan a silicon film surface. In this embodiment,laser light irradiation with repetition rate of 30 Hz and energy densityof 470 mJ/cm² is performed in the air.

Note that since laser light irradiation is performed in the air or in anoxygen atmosphere, an oxide film is formed on the surface by emittinglaser light. Note that an example in which the pulse laser is used isshown in this embodiment; however, a continuous wave laser may also beused, and in order to obtain crystal with large grain size at the timeof crystallization of a semiconductor film, it is preferable to use asolid laser which is capable of continuous oscillation and to apply thesecond to fourth harmonic wave of a fundamental wave. Typically, asecond harmonic wave (532 nm) or a third harmonic wave (355 nm) of anNd: YVO₄ laser (a fundamental wave of 1064 nm) may be applied.

In a case of using a continuous wave laser, laser light which is emittedfrom a continuous wave YVO₄ laser of 10 W output is converted into aharmonic wave by a non-linear optical element. Also, there is a methodby which YVO₄ crystal and a non linear optical element are put in anoscillator and a high harmonic wave is emitted. Then, the laser lighthaving a rectangular shape or an elliptical shape on an irradiatedsurface is preferably formed by an optical system to be emitted to anobject to be processed. At this time, the energy density ofapproximately 0.01 to 100 MW/cm² (preferably, 0.1 to 10 MW/cm²) isrequired. The semiconductor film may be moved at approximately a rate of10 to 2000 cm/s relatively with respect to the laser light so as to beirradiated.

Subsequently, in addition to the oxide film which is formed by the abovelaser light irradiation, a barrier layer formed of an oxide film havinga thickness of 1 to 5 nm in total is formed by treating the surface withozone water for 120 seconds. The barrier layer is formed in order toremove a catalytic element which is added for crystallization, forexample, nickel (Ni) from the film. Although the barrier layer is formedby using ozone water here, the barrier layer may be formed by stackingan oxide film having a thickness of approximately 1 to 10 nm by a methodof oxidizing a surface of a semiconductor film having a crystallinestructure by UV-ray irradiation under an oxygen atmosphere; a method ofoxidizing a surface of a semiconductor film having a crystallinestructure by oxygen plasma treatment; a plasma CVD method; a sputteringmethod; an evaporation method; or the like. Also, the oxide film whichis formed by laser light irradiation may be removed before forming thebarrier layer.

Then, an amorphous silicon film containing an argon element whichbecomes a gettering site is deposited to be 10 to 400 nm thick, here 100nm thick, is formed over the barrier layer by a sputtering method. Here,the amorphous silicon film containing an argon element is formed underan atmosphere containing an argon element with the use of a silicontarget. In a case where an amorphous silicon film containing argon isformed by a plasma CVD method, deposition conditions are as follows:flow ratio of monosilane to argon (SiH₄:Ar) is 1:99, deposition pressureis set to be 6.665 Pa, RF power density is set to be 0.087 W/cm², anddeposition temperature is set to be 350° C.

Thereafter, the amorphous silicon film is put in a furnace heated at650° C. and heat treatment is performed for 3 minutes to remove acatalytic element (gettering). Accordingly, the catalytic elementconcentration in the semiconductor film having a crystalline structureis reduced. A lamp annealing apparatus may be used instead of thefurnace.

Subsequently, the amorphous silicon film containing an argon element,which is a gettering site, is selectively removed by using the barrierlayer as an etching stopper, and thereafter, the barrier layer isselectively removed by rare hydrofluoric acid. Note that nickel has atendency to move to a region having high oxygen concentration at thetime of gettering; therefore, it is preferable that the barrier layerformed of an oxide film is removed after gettering.

Note that, in a case where crystallization with the use of a catalyticelement is not performed to a semiconductor film, the above steps suchas forming a barrier layer, forming the gettering site, heat treatmentfor gettering, removing the gettering site, and removing the barrierlayer are not required.

Subsequently, a thin oxide film is formed on the surface of the obtainedsemiconductor film having a crystalline structure (for example, acrystalline silicon film) with ozone water, and thereafter, a maskformed from a resist is formed using a first photomask and etchingtreatment into a desired shape is performed to form semiconductor films(in the present specification, referred to as an island-shapedsemiconductor region) 331 and 332 which are separated into an islandshape (FIG. 5A). After the island-shaped semiconductor region is formed,a mask formed from a resist is removed.

Next, a very small amount of an impurity element (boron or phosphorus)is added in order to control a threshold value of a TFT, if necessary.Here, an ion doping method is used, in which diborane (B₂H₆) is notseparated by mass but excited by plasma.

Subsequently, the oxide film is removed with etchant containinghydrofluoric acid, and at the same time, the surfaces of theisland-shaped semiconductor films 331 and 332 are washed. Thereafter, aninsulating film containing silicon as its main component which becomes agate insulating film 313 is formed. Here, a silicon oxide filmcontaining nitrogen (composition ratio Si=32%, O=59%, N=7%, and H=2%) isformed to have a thickness of 115 nm by a plasma CVD method.

Subsequently, after a metal film is formed over the gate insulating film313, patterning is performed using a second photomask to form gateelectrodes 334 and 335, wirings 314 and 315, and a terminal electrode350 (FIG. 5B). As the metal film, for example, a film is used, in whichtantalum nitride (TaN) and tungsten (W) are stacked to be 30 nm and 370nm, respectively.

As the gate electrodes 334 and 335, the wirings 314 and 315, and theterminal electrode 350, in addition to the above film, a single-layerfilm formed from an element selected from titanium (Ti), tungsten (W),tantalum (Ta), molybdenum (Mo), neodymium (Nd), cobalt (Co), zirconium(Zr), zinc (Zn), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium(Os), iridium (Ir), platinum (Pt), aluminum (Al), gold (Au), silver(Ag), and copper (Cu), or an alloy material or a compound materialcontaining the above element as its main component; or a single-layerfilm formed from nitride thereof, for example, titanium nitride,tungsten nitride, tantalum nitride or molybdenum nitride can be used.

Subsequently, an impurity imparting one conductivity type is introducedto the island-shaped semiconductor regions 331 and 332 to form a sourceregion or a drain region 337 of the TFT 113 and a source region or adrain region 338 of the TFT 112. In this embodiment, an n-channel TFT isformed; therefore, an n-type impurity, for example, phosphorus (P) orarsenic (As) is introduced to the island-shaped semiconductor regions331 and 332.

Next, a first interlayer insulating film (not shown) containing asilicon oxide film is formed to be 50 nm thick by a CVD method, andthereafter, a process is performed, in which the impurity element addedto each of the island-shaped semiconductor regions is activated. Thisactivation process is performed by a rapid thermal annealing method (RTAmethod) using a lamp light source; an irradiation method of a YAG laseror an excimer laser from the back side; heat treatment using a furnace;or a method which is a combination of any of the foregoing methods.

Then, a second interlayer insulating film 316 including a siliconnitride film containing hydrogen and oxygen is formed, for example, tobe 10 nm thick.

Subsequently, a third interlayer insulating film 317 formed of aninsulating material is formed over the second interlayer insulating film316 (FIG. 5D). An insulating film obtained by a CVD method can be usedfor the third interlayer insulating film 317. In this embodiment, inorder to improve adhesion, a silicon oxide film containing nitrogen isformed to be 900 nm thick as the third interlayer insulating film 317.

Then, heat treatment (heat treatment at 300 to 550° C. for 1 to 12hours, for example, at 410° C. for 1 hour) is performed to hydrogenatethe island-shaped semiconductor film. This process is performed toterminate a dangling bond of the island-shaped semiconductor film byhydrogen contained in the second interlayer insulating film 316. Theisland-shaped semiconductor film can be hydrogenated regardless ofwhether or not the gate insulating film 313 is formed.

In addition, as the third interlayer insulating film 317, an insulatingfilm using siloxane and a stacked structure thereof can also be used.Siloxane is composed of a skeleton structure of a bond of silicon (Si)and oxygen (O). A compound containing at least hydrogen (such as analkyl group or aromatic hydrocarbon) is used as a substituent. Fluorinemay also be used as a substituent. Moreover, fluorine and a compoundcontaining at least hydrogen may be used as a substituent.

In a case where an insulating film using siloxane and a stackedstructure thereof are used as the third interlayer insulating film 317,after forming the second interlayer insulating film 316, heat treatmentto hydrogenate the island-shaped semiconductor film can be performed,and then, the third interlayer insulating film 317 can be formed.

Subsequently, a mask formed from a resist is formed by using a thirdphotomask, and the first interlayer insulating film, the secondinterlayer insulating film 316 and the third interlayer insulating film317, or the gate insulating film 313 is selectively etched to form acontact hole. Then, the mask formed from a resist is removed.

Note that the third interlayer insulating film 317 may be formed ifnecessary. In a case where the third interlayer insulating film 317 isnot formed, the first interlayer insulating film, the second interlayerinsulating film 316, and the gate insulating film 313 are selectivelyetched to form a contact hole after forming the second interlayerinsulating film 316.

Next, after forming a metal stacked film by a sputtering method, a maskformed from a resist is formed by using a fourth photomask, and then,the metal film is selectively etched to form a wiring 319, a connectionelectrode 320, a terminal electrode 351, a source electrode or drainelectrode 341 of the TFT 112, and a source electrode or a drainelectrode 342 of the TFT 113. Then, the mask formed from a resist isremoved. Note that the metal film of this embodiment is a stacked layerin which three layers of a Ti film with a thickness of 100 nm, an Alfilm containing a very small amount of Si with a thickness of 350 nm,and a Ti film with a thickness of 100 nm are stacked.

In addition, as shown in FIG. 4B, in a case where each of a wiring 404,a connection electrode 405, a terminal electrode 401, a source electrodeor a drain electrode 402 of the TFT 112, and a source electrode or adrain electrode 403 of the TFT 113 is formed of a single-layerconductive film, a titanium film (Ti film) is preferable in terms ofheat resistance, conductivity, and the like. Instead of a titanium film,a single-layer film formed from an element selected from tungsten (W),tantalum (Ta), molybdenum (Mo), neodymium (Nd), cobalt (Co), zirconium(Zr), zinc (Zn), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium(Os), iridium (Ir) and platinum (Pt), or an alloy material or a compoundmaterial containing the above element as its main component, or asingle-layer film formed from nitride thereof, for example, titaniumnitride, tungsten nitride, tantalum nitride, or molybdenum nitride canbe used. The number of deposition can be reduced in the manufacturingprocess, by forming the wiring 404, the connection electrode 405, theterminal electrode 401, the source electrode or the drain electrode 402of the TFT 112, and the source electrode or the drain electrode 403 ofthe TFT 113 with a single-layer film.

The top gate TFTs 112 and 113 using a polycrystalline silicon film canbe manufactured by the process described above.

Subsequently, after forming a conductive metal film (such as titanium(Ti) or molybdenum (Mo)) which is not likely to be an alloy by reactingwith a photoelectric conversion layer (typically, amorphous silicon)which is formed later, a mask formed from a resist is formed by using afifth photomask, and then, the conductive metal film is selectivelyetched to form a protective electrode 318 which covers a wiring 319(FIG. 6A). Here, a Ti film having a thickness of 200 nm obtained by asputtering method is used. Note that the connection electrode 320, theterminal electrode 351, and the source electrode or the drain electrodeof the TFT are covered with a conductive metal film in the same manner.Therefore, the conductive metal film also covers a side face where thesecond Al film is exposed in these electrodes, and the conductive metalfilm also can prevent diffusion of an aluminum atom to the photoelectricconversion layer.

However, in a case where the wiring 319, the connection electrode 320,the terminal electrode 351, the source electrode or the drain electrode341 of the TFT 112, and the source electrode or the drain electrode 342of the TFT 113 are formed from a single-layer conductive film, that is,as shown in FIG. 4B, in a case where the wiring 404, the connectionelectrode 405, the terminal electrode 401, the source electrode or thedrain electrode 402 of the TFT 112, and the source electrode or thedrain electrode 403 of the TFT 113 are formed instead of theseelectrodes or wiring as shown in FIG. 4B, the protective electrode 318is not necessarily be formed.

Subsequently, a photoelectric conversion layer 111 including a p-typesemiconductor layer 111 p, an i-type semiconductor layer 111 i and ann-type semiconductor layer 111 n is formed over the third interlayerinsulating film 317.

The p-type semiconductor layer 111 p may be formed by depositing asemiamorphous silicon film containing an impurity element belonging toGroup 13 of the periodic table such as boron (B) by a plasma CVD method.

The wiring 319 and the protective electrode 318 are in contact with thelowest layer of the photoelectric conversion layer 111, in thisembodiment, the p-type semiconductor layer 111 p.

After the p-type semiconductor layer 111 p is formed, the i-typesemiconductor layer 111 i and the n-type semiconductor layer 111 n aresequentially formed. Accordingly, the photoelectric conversion layer 111including the p-type semiconductor layer 111 p, the i-type semiconductorlayer 111 i and the n-type semiconductor film 111 n is formed.

As the i-type semiconductor layer 111 i, for example, a semiamorphoussilicon film is formed by a plasma CVD method. In addition, as then-type semiconductor layer 111 n, a semiamorphous silicon filmcontaining an impurity element belonging to Group 15 of the periodictable, for example, phosphorus (P) may be formed, or after forming asemiamorphous silicon film, an impurity element belonging to Group 15 ofthe periodic table may also be introduced.

In addition, as the p-type semiconductor layer 111 p, the intrinsicsemiconductor layer 111 i and the n-type semiconductor layer 111 n, notonly a semiamorphous semiconductor film but also an amorphoussemiconductor film may be used.

Next, a sealing layer 324 formed from an insulating material (forexample, an inorganic insulating film containing silicon) is formed tohave a thickness of 1 to 30 μm over the entire surface to obtain a stateshown in FIG. 6B. Here, as an insulating material film, a silicon oxidefilm containing nitrogen with a thickness of 1 μm is formed by a CVDmethod. Improvement in adhesiveness is attempted by using an insulatingfilm formed by a CVD method.

Subsequently, after the sealing layer 324 is etched to provide anopening, terminal electrodes 121 and 122 are formed by a sputteringmethod. Each of the terminal electrodes 121 and 122 is a stacked layerof a titanium film (Ti film) (100 nm), a nickel film (Ni film) (300 nm),and a gold film (Au film) (50 nm). The thus obtained terminal electrode121 and the terminal electrode 122 have fixing intensity of more thanSN, which is sufficient fixing intensity as a terminal electrode.

By the process described above, the terminal electrode 121 and theterminal electrode 122 which can be connected by the solder are formed,and a structure shown in FIG. 6C can be obtained.

Next, a plurality of light detective portion chips is taken out bycutting separately. A large amount of light detective portion chips (2mm×1.5 mm) can be manufactured from one large-sized substrate (forexample, 600 cm×720 cm).

A cross-sectional view of one taken light detective portion chip (2mm×1.5 mm) is shown in FIG. 7A, a bottom view thereof is shown in FIG.7B, and a top view thereof is shown in FIG. 7C. In FIGS. 7A to 7C, thesame portions as those in FIGS. 4A to 4C, FIGS. 5A to 5C, and FIGS. 6Ato 6C are denoted by the same reference numerals. Note that the totalthickness including thicknesses of a substrate 310, an element formationregion 410, a terminal electrode 121 and a terminal electrode 122 is0.8+0.05 mm in FIG. 17A.

In addition, in order to reduce the total thickness of the lightdetective portion chip, the substrate 310 may be ground to be thinned byCMP treatment or the like, and then, cut separately by a dicer to takeout a plurality of light detective portion chips.

In FIG. 7B, each electrode size of the terminal electrodes 121 and 122is 0.6 mm×1.1 mm, and the interval between the electrodes is 0.4 mm. Inaddition, in FIG. 7C, the area of a light receiving portion 411 is 1.57mm². Moreover, an amplifier circuit portion 412 is provided withapproximately 100 TFTs.

Lastly, the obtained light detective portion chip is mounted on amounting surface of a substrate 360. Note that in order to connect theterminal electrode 121 to an electrode 361 and the terminal electrode122 to an electrode 362, solders 364 and 363 are respectively used. Thesolders are formed in advance by a screen printing method or the likeover the electrodes 361 and 362 of the substrate 360. Then, after thesolder and the terminal electrode are made in an abutted state, solderreflow treatment is performed to mount the light sensor chip on thesubstrate. The solder reflow treatment is performed at approximately 255to 265° C. for about 10 seconds in an inert gas atmosphere, for example.Alternatively, a bump formed from metal (such as gold or silver), a bumpformed from a conductive resin, or the like can be used instead of thesolder. Further alternatively, a lead-free solder may be used formounting in consideration of environmental problems.

Note that this embodiment can be combined with any description inEmbodiment Mode and Embodiment 1.

Embodiment 3

In this embodiment, an example in which an amplifier circuit is formedfrom a p-channel TFT will be described with reference to FIG. 3 andFIGS. 8A and 8B. Note that the same portions as those in Embodiment Modeand Embodiment 2 are denoted by the same reference numerals, and theamplifier circuit may be formed on the basis of the manufacturingprocess described in Embodiment Mode and Embodiment 2.

In a case where an amplifier circuit, for example, a current mirrorcircuit 203 is formed from p-channel TFTs 201 and 202, a p-typeimpurity, for example, boron (B) may be substituted for the impurityimparting one conductivity type to the island-shaped semiconductorregion in Embodiment Mode and Embodiment 2.

A view of an equivalent circuit of a light detective portion of thisembodiment in which the current mirror circuit 203 is formed from thep-channel TFTs 201 and 202 is shown in FIG. 3, and a cross-sectionalview thereof is shown in FIGS. 8A and 8B. Note that FIG. 8B is a view inwhich the vicinity of the p-channel TFTs 201 and 202 and a photoelectricconversion layer 204 of FIG. 8A is enlarged.

In FIG. 3 and FIGS. 8A and 8B, terminal electrodes 221 and 222 areconnected to the photoelectric conversion layer 204 and the p-channelTFTs 201 and 202, respectively. The p-channel TFT 201 is electricallyconnected to an electrode at an anode side of the photoelectricconversion layer 204. After an n-type semiconductor layer 204 n, ani-type semiconductor layer 204 i, and a p-type semiconductor layer 204 pare sequentially stacked over a second electrode (the electrode at theanode side) which is connected to the p-channel TFT 201, a firstelectrode (an electrode at a cathode side) may be formed; accordingly,the photoelectric conversion layer 204 is formed.

In addition, a photoelectric conversion layer in which the stackingorder is reversed may also be used. After the p-type semiconductorlayer, the i-type semiconductor layer and the n-type semiconductor layerare sequentially stacked over the first electrode (the electrode at thecathode side), the second electrode (the electrode at the anode side)which is connected to the p-channel TFT 201 may be formed and theterminal electrode at the cathode side which is connected to the firstelectrode may also be formed.

As shown in FIG. 8B, a p-type impurity, for example, boron (B) isintroduced to an island-shaped semiconductor region 231 of the p-channelTFT 201 and an island-shaped semiconductor region 232 of the p-channelTFT 202. A source region or drain region 241 is formed in the p-channelTFT 201, and a source region or a drain region 242 is formed in thep-channel TFT 202.

In FIGS. 8A and 8B, instead of a wiring 319 and a protective electrodethereof 318; a connection electrode 320 and a protective electrodethereof 264; a terminal electrode 351 and a protective electrode thereof263; a source electrode or a drain electrode 251 of the TFT 201 and aprotective electrode thereof 261; and a source electrode or a drainelectrode 252 of the TFT 202 and a protective electrode thereof 262,each wiring and electrode may also be formed by using a single-layerconductive film in the same manner as the wiring 404, the connectionelectrode 405, the terminal electrode 401, the source electrode or thedrain electrode 402 of the TFT 112 and the source electrode or the drainelectrode 403 of the TFT 113 shown in FIG. 4B.

Note that this embodiment mode can be combined with any description inEmbodiment Mode, Embodiment 1 and Embodiment 2.

Embodiment 4

In this embodiment, an example of a light detective portion in which anamplifier circuit is formed by using a bottom gate TFT and amanufacturing method thereof will be described with reference to FIGS.9A to 9E, FIGS. 10A to 1C and FIG. 11. Note that the same portions asthose in Embodiment Mode, Embodiment Mode 2 and Embodiment Mode 3 aredenoted by the same reference numerals.

First, a base insulating film 312 and a metal film 511 are formed over asubstrate 310 (FIG. 9A). As the metal film 511, in this embodiment,tantalum nitride (TaN) having a thickness of 30 nm and tungsten (W)having a thickness of 370 nm are stacked is used, for example.

In addition, as the metal film 511, in addition to the above film, asingle-layer film formed from an element selected from titanium (Ti),tungsten (W), tantalum (Ta), molybdenum (Mo), neodymium (Nd), cobalt(Co), zirconium (Zr), zinc (Zn), ruthenium (Ru), rhodium (Rh), palladium(Pd), osmium (Os), iridium (Ir), platinum (Pt), aluminum (Al), gold(Au), silver (Ag) and copper (Cu), or an alloy material or a compoundmaterial containing the above element as its main component, or asingle-layer film formed from nitride thereof such as titanium nitride,tungsten nitride, tantalum nitride, or molybdenum nitride can be used.

Note that the metal film 511 may be formed directly on the substrate 310without forming the base insulating film 312 on the substrate 310.

Next, the metal film 511 is patterned to form gate electrodes 512 and513, wirings 314 and 315 and a terminal electrode 350 (FIG. 9B).

Subsequently, a gate insulating film 514 which covers the gateelectrodes 512 and 513, the wirings 314 and 315 and the terminalelectrode 350 is formed. In this embodiment, the gate insulating film514 is formed by using an insulating film containing silicon as its maincomponent, for example, a silicon oxide film containing nitrogen(composition ratio Si=32%, O=59%, N=7%, H=2%) having a thickness of 115nm by a plasma CVD method.

Next, island-shaped semiconductor regions 515 and 516 are formed overthe gate insulating film 514. The island-shaped semiconductor regions515 and 516 may be formed by the similar material and manufacturingprocess to those of the island-shaped semiconductor regions 331 and 332described in Embodiment 2 (FIG. 9C).

After the island-shaped semiconductor regions 515 and 516 are formed, amask 518 is formed covering portions except for regions whichsequentially becomes a source region or a drain region 521 of a TFT 502and a source region or a drain region 522 of a TFT 501 to introduce animpurity imparting one conductivity type (FIG. 9D). As the oneconductivity type impurity, in a case of forming an n-channel TFT,phosphorus (P) or arsenic (As) may be used as an n-type impurity,whereas in a case of forming a p-channel TFT, boron (B) may be used as ap-type impurity. In this embodiment, phosphorus which is an n-typeimpurity is introduced to the island-shaped semiconductor regions 515and 516, and then, a channel formation region is formed between thesource region or the drain region 521 and the source region or the drainregion 521 of the TFT 502, and a channel formation region is formedbetween the source region or the drain region 522 and a source region ora drain region 522 of the TFT 501.

Next, the mask 518 is removed, and a first interlayer insulating filmwhich is not shown, a second interlayer insulating film 316 and a thirdinterlayer insulating film 317 are formed (FIG. 9E). A material and amanufacturing process of the first interlayer insulating film, thesecond interlayer insulating film 316 and the third interlayerinsulating film 317 is based on the description in Embodiment Mode 2.

Contact holes are formed in the first interlayer insulating film, thesecond interlayer insulating film 316 and the third interlayerinsulating film 317, and a metal film is formed, and further, the metalfilm is selectively etched to form a wiring 319, a connection electrode320, a terminal electrode 351, a source electrode or a drain electrode531 of the TFT 502 and a source electrode or a drain electrode 532 ofthe TFT 501. Then, the mask formed from a resist is removed. Note thatthe metal film of this embodiment is a film in which 3 layers of a Tifilm having a thickness of 100 nm, an Al film containing a very smallamount of silicon having a thickness of 350 nm and a Ti film having athickness of 100 nm are stacked.

In addition, instead of the wiring 319 and a protective electrodethereof 318; the connection electrode 320 and a protective electrodethereof 533; the terminal electrode 351 and a protective electrodethereof 538; the source electrode or the drain electrode 531 of the TFT502 and a protective electrode thereof 536; and a source electrode or adrain electrode 252 of a TFT 202 and a protective electrode thereof 537,each wiring and electrode may be formed by using a single-layerconductive film, in the same manner as the wiring 404, the connectionelectrode 405, the terminal electrode 401, the source electrode or thedrain electrode 402 of the TFT 112 and the source electrode or the drainelectrode 403 of the TFT 113 in FIG. 4B.

Through the above process, bottom gate TFTs 501 and 502 can bemanufactured.

Subsequently, a photoelectric conversion layer 111 including a p-typesemiconductor layer 111 p, an i-type semiconductor layer 111 i and ann-type semiconductor layer 111 n is formed over the third interlayerinsulating film 317 (FIG. 10B). Embodiment Mode and Embodiment 2 may bereferred for a material and a manufacturing process of the photoelectricconversion layer 111.

Next, a sealing layer 324 and terminal electrodes 121 and 122 are formed(FIG. 10C). The terminal electrode 121 is connected to the n-typesemiconductor layer 111 n, and the terminal electrode 122 is formed bythe same process as the terminal electrode 121.

Moreover, a substrate 360 having electrodes 361 and 362 is mounted bysolders 364 and 363. Note that the electrode 361 over the substrate 360is mounted on the terminal electrode 121 by the solder 364. In addition,the electrode 362 over the substrate 360 is mounted on the terminalelectrode 122 by the solder 363.

In a light detective portion shown in FIG. 11, light which enters aphotoelectric conversion layer 111 enters mainly from a substrate 310site, whereas light which enters inversely staggered TFTs 501 and 502enters mainly from the substrate 360 side. In addition, by forming agate electrode with a transparent conductive film, light which entersfrom the substrate side can be detected.

Note that this embodiment can be combined with any description inEmbodiment Mode and Embodiments 1 to 3.

Embodiment 5

In this embodiment, an example in which a housing is formed to aphotoelectric conversion device of the present invention to control anincidence direction of light will be described with reference to FIGS.12A and 12B and FIGS. 13A and 13B.

In FIG. 12A, a housing 601 is formed to the photoelectric conversiondevice of FIG. 4A so that light which enters a photoelectric conversionlayer 111 enters not from a substrate 310 side but from a substrate 360side. The housing 601 is provided with openings that are formed in aregion where TFTs 112 and 113 are formed at the substrate 310 side and aregion where the photoelectric conversion layer 111 is formed at thesubstrate 360 side.

In FIG. 12A, there are a terminal electrode 121, an electrode 361 and asolder 364; however, light which enters from the substrate 360 sideenters diagonally through a sealing layer 324. Accordingly, aphotoelectric current can be generated and light can be detected.

In addition, any material can be used for the housing 601 and housings602 to 604 that are described below as long as it has function ofshielding light. For example, a resin material or the like having ametal material or a black pigment may be used.

In FIG. 12B, the housing 602 is formed to the light detective portion ofFIG. 11 so that light which enters the photoelectric conversion layer111 enters not from the substrate 310 side but from the substrate 360side. The housing 602 is provided with an opening which is formed in aregion where TFTs 501 and 502 are formed and a region where thephotoelectric conversion layer 111 is formed at the substrate 360 side.

Also in FIG. 12B, similarly to FIG. 12A, light which enters from thesubstrate 360 side enters diagonally the photoelectric conversion layer111 through the sealing layer 324. Accordingly, a photoelectric currentcan be generated and light can be detected.

In FIG. 13A, a housing 603 is formed to the light detective portion ofFIG. 4A so that light which enters a photoelectric conversion layer 111and TFTs 112 and 113 enters not from the substrate 310 side but from thesubstrate 360 side. The housing 603 is provided with an opening which isformed in a region where TFTs 501 and 502 are formed and a region wherethe photoelectric conversion layer 111 is formed at the substrate 360side.

In FIG. 13A, there is a gate electrode between incident light and anisland-shaped semiconductor region in each of the TFTs 112 and 113;however, light which does not pass through the gate electrode amonglight which enters from the substrate 360 side enters the island-shapedsemiconductor regions of the TFTs 112 and 113. In addition, light whichenters from the substrate 360 side enters diagonally the photoelectricconversion layer 111 thorough a sealing layer 324. Accordingly, aphotoelectric current can be generated and light can be detected.

In FIG. 13B, a housing 604 is formed to the light detective portion ofFIG. 11 so that light which enters the photoelectric conversion layer111 enters not from a substrate 310 side but from a substrate 360 side,and moreover, light which enters TFTs 501 and 502 enters not from thesubstrate 360 side but from the substrate 310. The housing 604 isprovided with openings that are formed in a region where the TFTs 501and 502 are formed at the substrate 310 side and a region where thephotoelectric conversion layer 111 is formed at the substrate 360 side.

In FIG. 13B, there is a gate electrode between incident light and anisland-shaped semiconductor region in each of the TFTs 501 and 502;however, light which does not pass through the gate electrode enters theisland-shaped semiconductor region of the TFTs 501 and 502. Accordingly,a photoelectric current can be generated and light can be detected. Inaddition, light which enters from the substrate 360 side entersdiagonally the photoelectric conversion layer 111 through a sealinglayer 324; accordingly, a photoelectric current can be generated andlight can be detected.

Note that this Embodiment can be combined with any description inEmbodiment Mode and Embodiments 1 to 4.

Embodiment 6

In this embodiment, a circuit which switches a power source (bias) as abias switching means will be described with reference to FIG. 22, FIG.23, FIG. 25, FIG. 26 and FIG. 27.

In FIG. 22 and FIG. 23, reference numeral 901 denotes a photo sensoroutput V_(PS), 902; a reference voltage generating circuit to determinea reference voltage V_(r), 903; a comparator, and 904; an output bufferhaving a first stage 904 a, a second stage 904 b and a third stage 904c. In FIG. 22, only three stages of the output buffer are described;however, four or more stages of the output buffer can be provided, oralternatively, only one stage of the output buffer can be provided. Inaddition, reference numeral 905 denotes internal resistor of a TFT of acurrent mirror circuit.

FIG. 23 shows a specific circuit configuration of FIG. 22, and thecomparator 903 has p-channel TFTs 911 and 913, n-channel TFTs 912 and914 and a resistor 921. Also, the reference voltage generating circuit902 has resistors 923 and 924. In addition, in FIG. 23, the first stage904 a of the output buffer 904 is shown, and the first stage 904 a ofthe output buffer 904 is formed from a p-channel TFT 915 and ann-channel TFT 916. In FIG. 23, an n-channel TFT is a single gate TFTwhich has one gate electrode; however, in order to reduce an offcurrent, the n-channel TFT may be formed of a multi gate TFT which has aplurality of gate electrodes, for example, a double gate TFT which hastwo gate electrodes. Note that the other stages may be formed in thesame circuit as 904 a.

In FIG. 23, the first stage 904 a of the output buffer 904 may besubstituted for a circuit 942 shown in FIG. 26A and a circuit 944 shownin FIG. 26B. The circuit 942 shown in FIG. 26A is formed from ann-channel TFT 916 and a p-channel TFT 941, and the circuit shown in FIG.26B is formed from n-channel TFTs 916 and 943.

Note that an output voltage V₀ of the current mirror circuit may be usedfor the photo sensor V_(PS), and a voltage in which the output voltageV₀ of the current mirror circuit is amplified in an amplifier circuitmay also be used.

In the circuit shown in FIG. 22, when the output voltage V₀ of thecurrent mirror circuit reaches a certain value, a power source voltageof the current mirror circuit is reversed. The circuit shown in FIG. 22reverses the power source in a case where the output voltage exceedsV_(r), having the reference voltage V_(r) as a boundary. In FIG. 23, thereference voltage V_(r) is determined by the reference voltagegenerating circuit 902. In addition, the reference voltage Vr may usevoltage which is applied to a load by a current in which current amountgenerated when a photo sensor receives light of 100 1× is amplified bythe current mirror circuit.

In FIG. 23, the reference voltage V_(r) is determined by the referencevoltage generating circuit; however, the reference voltage V_(r) may bedirectly inputted from an external circuit 931 (FIG. 25A), or inputtedfrom a circuit 932 selecting several input voltage by using a selector(an analog switch or the like) (FIG. 25B).

In addition, in the circuit shown in FIG. 23, the reference voltageV_(r) is required to be more than a threshold voltage (V_(th)≦V_(r) whenthe threshold voltage is V_(th)) of a TFT which is included in thecomparator. It is necessary that the reference voltage or the photosensor output voltage V_(PS) is adjusted so as to satisfy this voltage.

The photo sensor output V_(PS) is inputted to the gate electrode of thep-channel TFT 911 of the comparator 903, and is compared with a voltagevalue from the reference voltage generating circuit 902. In a case wherethe photo sensor output V_(PS) is lower than a voltage value from thereference voltage generating circuit, the photo sensor output V_(PS) isconnected to a power source 103 a of a power source 103, and a currentflows in a direction shown in FIG. 27A. In addition, in a case where thephoto sensor output V_(PS) is higher than a voltage value from thereference voltage generating circuit, the photo sensor output V_(PS) isconnected to a power source 103 b of the power source 103, and a currentflows in a direction shown in FIG. 27B.

Embodiment 7

In this embodiment, an example in which a light detective portion whichis obtained by the present invention is incorporated to variouselectronic devices will be described. As an electronic device to whichthe present invention is applied, a computer, a display, a cellularphone, a TV set or the like are given. Specific examples of thoseelectronic devices are shown in FIG. 14, FIGS. 15A and 15B, FIGS. 16Aand 16B and FIG. 17.

FIG. 14 shows a cellular phone including a main body (A) 701, a mainbody (B) 702, a housing 703, operation keys 704, an audio output portion705, an audio input portion 706, a circuit substrate 707, a displaypanel (A) 708, a display panel (B) 709, a hinge 710, alight-transmitting material portion 711 and a light detective portion712. The present invention can be applied to the light detective portion712.

The light detective portion 712 detects light which transmits thelight-transmitting material portion, controls luminance of the displaypanel (A) 708 and the display panel (B) 709 in accordance withilluminance of detected external light, or controls illumination of theoperation keys 704 in accordance with illuminance which is obtained bythe light detective portion 712. Accordingly, current consumption of acellular phone can be suppressed.

FIGS. 15A and 15B show another example of a cellular phone. In FIGS. 15Aand 15B, reference numeral 721 denotes a main body, 722; housing, 723; adisplay panel, 724; operation keys, 725; an audio output portion, 726;an audio input portion, and 727 and 728; light detective portions.

In a cellular phone shown in FIG. 15A, luminance of the display panel723 and the operation keys 724 can be controlled by detecting externallight by the light detective portion 727 which is provided at the mainbody 721.

Also, in a cellular phone shown in FIG. 15B, in addition to thestructure of FIG. 15A, the light detective portion 728 is providedinside the main body 721. By the light detective portion 728, luminanceof backlight provided at the display portion 723 can be detected.

FIG. 16A shows a computer including a main body 731, a housing 732, adisplay portion 733, a keyboard 734, an external connection port 735, apointing mouse 736 and the like.

FIG. 16B shows a display device, and a television receiver or the likecorresponds to this. The display device includes a housing 741, asupporting base 742, a display portion 743, and the like.

As the display portion 733 which is provided for the computer of FIG.16A and the display portion 743 of the display device shown in FIG. 16B,a specific structure in a case of using a liquid crystal panel is shownin FIG. 17.

A liquid crystal panel 762 shown in FIG. 17 is incorporated in a housing761, and includes substrates 751 a and 751 b, a liquid crystal layer 752sandwiched between the substrates 751 a and 751 b, polarized filters 752a and 752 b, a backlight 753, and the like. A light detective portion754 is formed at the housing 761.

The light detective portion 754 which is manufactured by using thepresent invention detects the light amount from the backlight 753, andluminance of the liquid crystal panel 762 is adjusted when informationthereof is fed back.

FIGS. 18A and 18B are views each showing an example in which the lightdetective of the present invention is incorporated in a camera, forexample, a digital camera. FIG. 18A is a front perspective view of thedigital camera, and FIG. 18B is a back perspective view of the digitalcamera. In FIG. 18A, the digital camera is provided with a releasebutton 801, a main switch 802, a finder window 803, a flush 804, a lens805, a camera cone 806, and a housing 807.

In addition, in FIG. 18B, a finder eyepiece window 811, a monitor 812and operation buttons 813 are provided.

When the release button 801 is held down to the half position, focusingmechanism and exposure mechanism are operated, and when the releasebutton is held down to the lowest position, a shutter is opened.

The main switch 802 switches ON or OFF of a power source of a digitalcamera by holding down or rotating.

The finder window 803 is placed at the upper portion of the front lens805 of the digital camera, and is a device for recognizing an area whichis taken or a focus position from the finder eyepiece window 811 shownin FIG. 18B.

The flush 804 is placed at the upper portion of the anterior surface ofthe digital camera, and when object luminance is low, supporting lightis emitted concurrently with the opening of the shutter by being helddown.

The lens 805 is placed at the front face of the digital camera. The lensis formed of a focusing lens, a zoom lens, or the like, and forms aphotographing optical system with a shutter and an aperture that are notshown. In addition, an image pickup device such as CCD (Charge CoupledDevice) is provided at the rear of the lens.

The camera cone 806 moves a lens position to adjust the focus of thefocusing lens, the zoom lens, and the like. When shooting, the cameracone is slid out to move the lens 805 forward. In addition, whencarrying it, the lens 805 is moved backward to be compact. Note that astructure is employed in this embodiment, in which the object can beshot by zooming by sliding out the camera cone; however, a structure isnot limited thereto, and a structure may also be employed, in whichshooting can be conducted by zooming without sliding out the camera coneby a photographing optical system inside the housing 807.

The finder eyepiece window 811 is provided at the upper portion of therear surface of the digital camera, for looking through when checking anarea which is taken or a focus point.

The operation buttons 813 are buttons for various functions that areprovided at the rear surface of the digital camera and include a set upbutton, a menu button, a display button, a functional button, aselection button, and the like.

When the light detective portion of the present invention isincorporated in the camera shown in FIGS. 18A and 18B, the lightdetective portion can detect whether or not light exists and the lightintensity, and accordingly, an exposure adjustment or the like of thecamera can be performed.

In addition, the light detective portion of the present invention can beapplied to other electronic devices, for example, a projection TV and anavigation system. That is, the light sensor of the present inventioncan be used for any device which is required to detect light.

Note that this embodiment can be combined with any description inEmbodiment Mode, and Embodiments 1 to 6.

By the present invention, a photoelectric conversion device which candetect a wide range of light intensity ranging from weak light to stronglight can be manufactured. In addition, by incorporating thephotoelectric conversion device of the present invention, an electronicdevice having high reliability can be obtained.

This application is based on Japanese Patent Application serial No.2005-148864 filed in Japan Patent Office on May 23 in 2005, the entirecontents of which are hereby incorporated by reference.

1. A photoelectric conversion device comprising: a photodiode comprisinga photoelectric conversion layer; an amplifier circuit comprising a thinfilm transistor; and a bias switching circuit, wherein the biasswitching circuit is configured to change a bias direction applied tothe photodiode and the amplifier circuit at a predetermined intensity ofincident light, and light which is less than the predetermined intensityis detected by the photodiode and light which is more than thepredetermined intensity is detected by the thin film transistor of theamplifier circuit.
 2. The photoelectric conversion device according toclaim 1, wherein the photoelectric conversion layer comprises a p-typesemiconductor layer, an i-type semiconductor layer and an n-typesemiconductor layer.
 3. The photoelectric conversion device according toclaim 1, wherein the thin film transistor comprises a source region or adrain region, a channel formation region, a gate insulating film and agate electrode.
 4. The photoelectric conversion device according toclaim 1, wherein the photodiode and the amplifier circuit are formedover a light-transmitting substrate.
 5. The photoelectric conversiondevice according to claim 1, wherein a direction of incident light whichis detected by the photodiode is the same as a direction of incidentlight which is detected by the thin film transistor.
 6. Thephotoelectric conversion device according to claim 1, wherein the thinfilm transistor is a top gate thin film transistor.
 7. The photoelectricconversion device according to claim 1, wherein a direction of incidentlight which is detected by the photodiode and a direction of incidentlight which is detected by the thin film transistor are opposite to eachother, with a substrate as the center.
 8. The photoelectric conversiondevice according to claim 1, wherein the thin film transistor is abottom gate thin film transistor.
 9. A method for driving aphotoelectric conversion device comprising: a photodiode having aphotoelectric conversion layer; an amplifier circuit including a thinfilm transistor; and a bias switching circuit, the method comprising thesteps of: switching a bias direction which is applied to the photodiodeand the amplifier circuit by the bias switching circuit at apredetermined intensity of incident light, and detecting light which isless than the predetermined intensity by the photodiode or light whichis more than the predetermined intensity by the thin film transistor ofthe amplifier circuit.
 10. The method for driving a photoelectricconversion device according to claim 9, wherein the photoelectricconversion layer comprises a p-type semiconductor layer, an i-typesemiconductor layer, and an n-type semiconductor layer.
 11. The methodfor driving a photoelectric conversion device according to claim 9,wherein the photodiode and the amplifier circuit are formed over alight-transmitting substrate.
 12. The method for driving a photoelectricconversion device according to claim 9, wherein a direction of incidentlight which is detected by the photodiode is the same as a direction ofincident light which is detected by the thin film transistor.
 13. Themethod for driving a photoelectric conversion device according to claim9, wherein a direction of incident light which is detected by thephotodiode and a direction of incident light which is detected by thethin film transistor are opposite to each other, with a substrate as thecenter.
 14. A photoelectric conversion device comprising: a photodiode;an amplifier circuit comprising a first transistor and a secondtransistor, wherein a gate of the first transistor is electricallyconnected to a gate of the second transistor, one of a source and adrain of the first transistor is electrically connected to the gate ofthe first transistor and one terminal of the photodiode, one of a sourceand a drain of the second transistor and the other terminal of thephotodiode are electrically connected to each other at a first node, andthe other of the source and the drain of the first transistor and theother of the source and the drain of the second transistor areelectrically connected to each other at a second node; and a biasswitching circuit, wherein the bias switching circuit is configured tochange a bias direction applied between the first node and the secondnode.
 15. The photoelectric conversion device according to claim 14,wherein the bias switching circuit is configured to change the biasdirection according to intensity of incident light.
 16. Thephotoelectric conversion device according to claim 14, wherein thetransistor is a thin film transistor.
 17. The photoelectric conversiondevice according to claim 14, wherein the photodiode comprises a p-typesemiconductor layer, an i-type semiconductor layer and an n-typesemiconductor layer.